cyberstrikeus CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0 - Control 4.4.2.1
Profile
- Level: Level 1 - Server, Level 1 - Workstation
- Assessment Status: Automated
Description
A default deny all policy on connections ensures that any unconfigured network usage will be rejected.
Notes:
- Changing firewall settings while connected over network can result in being locked out of the system
- Remediation will only affect the active system firewall, be sure to configure the default policy in your firewall management to apply on boot as well
Rationale
With a default accept policy the firewall will accept any packet that is not configured to be denied. It is easier to allow list acceptable usage than to deny list unacceptable usage.
Audit Procedure
Command Line
Run the following command and verify that the policy for the INPUT, OUTPUT, and FORWARD chains is DROP or REJECT:
iptables -L -n
Chain INPUT (policy DROP)
Chain FORWARD (policy DROP)
Chain OUTPUT (policy DROP)
Expected Result
Chain INPUT (policy DROP)
Chain FORWARD (policy DROP)
Chain OUTPUT (policy DROP)
Remediation
Command Line
Run the following commands to implement a default DROP policy:
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP
Default Value
Not applicable.
References
- NIST SP 800-53 Rev. 5: CA-9, SC-7
CIS Controls
v8 - 4.4 Implement and Manage a Firewall on Servers v8 - 4.5 Implement and Manage a Firewall on End-User Devices v7 - 9.4 Apply Host-based Firewalls or Port Filtering
MITRE ATT&CK Mappings: T1562, T1562.004 | TA0011 | M1031, M1037